IlALnKUT — The Acarina of the Seashore. 107 



a more exact study of tlie fauna. It was finally decirlod to adopt as a 

 preliniiuaiy sub-division the zones occupied by certain licliens and seaweeds. 

 Wiiere there is sufficient foothold for the dominant plants these zones arc 

 usually present, and succeed each other as well-defined hands on tlie seashore. 

 Beginning at the tup and descending, tlie zones occur in llie following order: 



The Orange Lichen zone (species of Physcia, Lccanora, &c.). 



The Pelvetia zone {Pelvctia caiialiculatn dominant). 



The Spiralis zone {Fiieus spiralis dominant). 



The Vesiculosus zone (Fucus vesiculoms dominant). 



The Serratus zone {Fucus scrraUis dominant). 



The two uppermost zones were the most thoroughly examined, partly on 

 account of their interest as a meeting-place of many terrestrial and maritinie 

 forms, and also their accessibility as less frequently covered by the tides. 

 They represent approximately the part of the shore lying between high neap 

 and high spring tides ; and it follows that during the period of neap tides 

 these two zones may be left uncovered for days ; for this reason they are 

 frequently almost dry, and the animals occurring therein must be capable of 

 withstanding conditions varying from time to time within a wide range. 



The Orange Lichen zone is bounded seawards by the Pelvetia zone. The 

 landward limit is vaguely defined by the extreme range of the maritime 

 species and the occurrence of purely terrestrial forms. In practice, however, 

 there is usually little difficulty in demarcating it. The width of the various 

 zones depends chiefly on the slope of the shore seawards. The more sheltered 

 the coast, the more clearly they are defined. 



Apart from descriptions of single species, the Acarina of the seashore ha\e 

 been but little studied, and such papers as have appeared on the subject are 

 of limited scope. Excluding the family Halacaridae or maiine mites, the 

 following papers are noteworthy, as they contain references to the great 

 majority of the intertidal Acarina. The numbers refer to the bibliography at 

 end of this paper : — Barrois (1), Berlese and Trouessart :20', Brady (21, 22). 

 Ilalbert (25), Hull 26 , King (27), Laboulbene (30), Lohmann (32, 34), 

 Michael (36, 37 , Moniez 38), Tietze (46), Topsent and Trouessart (47), 

 Tragardh (50), Trouessart (53). 



The first paper in which an attempt is made to deal comprehensively with 

 littoral species is that of Moniez (38) on the mites and insects observed by 

 him on the seashore at Boulogne; with the exception of a few unnamed 

 varieties the paper refers to previously known species. In 1SS9 Berlese and 

 Trouessart published a joint paper (20) containing the original descriptions of 

 six of our most characteristic shore mites. Ten yeais later 'J'ietze 46j made 

 observations on a few species found on the Venetian coast, and his j>aper 



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